Head locking apparatus in a servo system so that the head can read and write data on a tape without servo trucks

ABSTRACT

A tape drive which may accommodate tapes having a servo control track thereon as well as tapes without such tracks advantageously uses a lockout to prevent unwanted head translation when operating in an open loop mode. The lockout may be accomplished by energizing a voice coil motor to fix the head position, driving the voice coil motor to a fixed stop positioning the head, or latching a rocker connected to the head, thereby preventing movement of the head. The latching/unlatching function may be accomplished by driving an actuator supporting the beam springs, head and latch to an end-of-track position to similarly unlatch the rocker and return the assembly to a servo controlled mode of operation.

RELATED PATENT APPLICATIONS

This application is related to U.S. patent application Ser. No.08/489,462 filed on even date herewith, titled: Actuator For ServoActuated Tape Drive, by Eric. A. Eckberg et al. U.S. patent applicationSer. No. 08/474,227 filed on even date herewith, titled: Hybrid ActuatorServo Actuated Tape Drive, by Eric. A. Eckberg et al. and U.S. patentapplication Ser. No. 08/484,626 filed on even date herewith, titled:Mechanical Drive Enclosure For High Performance Tape Drive, by Eric. A.Eckberg et al.

FIELD OF THE INVENTION

This invention relates to tape drives for data recording andspecifically to the recording of very high density data on magnetic tapein a reliable manner so that the data may be retrieved with a highdegree of accuracy.

BACKGROUND OF THE INVENTION

Data storage on magnetic tape is well known and tape recorders have beenused to record data tracks on magnetic tape. However, the previoustechnique to record data in a plurality of parallel data tracks on themagnetic tape was to position the head relative to the tape path bymoving the read/write head relative to the tape to different trackpositions as desired and then holding the read/write head stationary. Insuch a system, the tape tracks must both be sufficiently wide andseparated to guarantee that the exposure of the data track to the headis accurate at least to the minimum requirements necessary to reliablyread and write the data. The read/write head is positioned at apredetermined fixed point, relative to the magnetic tape path and thedata track must accommodate variations of recording track location andtape location variances as the tape feeds past the head. Historically,this accommodation has been accomplished insuring that the track widthand the data track separation on the magnetic tape are sufficient forthe read/write head to remain positioned over the designated track andat the same time not read magnetically recorded signals from an adjacenttrack. This arrangement of track width and track separation willaccommodate any deviation of the track location from the design normeither due to being recorded on a first recorder and played orrerecorded on a second recorder or due to the wander of the tape as itis spooled past the read/write head from one spool to the other spool ofa cartridge.

The definition of the magnetic read/write head and the track width andseparations effectively limits the number of data tracks that may berecorded on any given width of tape. Reliance solely on the track widthand track separations to insure reliable read/write operations resultsin a significant waste of magnetic tape surface and thus limits the datadensity on the tape.

Whenever the positional requirements of the system are satisfied, theresulting track width and spacing clearly limits the number of datatracks. Data may be recorded in tracks that are much narrower and stillbe reliable from a read/write standpoint, but the read/write head mustbe and remain perfectly aligned with the data track. However, as thetrack width and the read/write head width narrow in an effort toincrease the data capacity of a given tape area, any misalignment of thehead with the track may lead to read/write repeatability failures andlost data. Thus, the resolution of the head placement mechanism and theprecision of the placement of the tape relative to the read/write headbecome limiting factors affecting the recording density of data on themagnetic tape surface in tape drives having static read/write heads.

In order to overcome the limitation in data density described above, thealignment of the magnetic tape data recording track relative to theread/write head gap of the read/write head must be greatly improved orcontrolled. Since it is not as practical to attempt to control the tapepath and the data track position based on tape position, the choicedevolves to controlling the read/write head more precisely and on aresponsive basis.

Efforts to control the head of a tape drive on a real-time basis tomaintain the head/data track alignment use a servo control to finelyposition the head relative to the coarse positioning of the steppermotor drive that drives the head carriage to a detented or staticposition.

In order to position the head precisely relative to a moving data trackon tape, a servo read/write head positioning drive is incorporated intothe tape drive system. The servo drive parameters of a high density tapecartridge are set forth in a QIC development standard, QIC-139, Rev. G.,31 Aug. 1994, published by Quarter-Inch Cartridge Drive Standards, Inc.,311 East Carrillo St., Santa Barbara, Calif. 93101. Among other criteriathis standard defines a pattern of servo tracks and data tracks thatmust be adhered to insure compatibility of the cartridges recorded onone recorder and read on another recorder. To provide the locationalcontrol of the servo read/write head positioning drive, a magnetic readhead gap may be placed at a position relative to a servo track on thetape. Then the read head gap is further moved to detect the edge of theservo control track (servo track) recorded on the tape. The read headwill provide signals which may be used to indicate the head locationrelative to the servo track. By using these signals as a basis, theservo control then may produce a positioning signal to drive a servopositioner. The servo positioner moves the read head, causing the readhead to track or follow the edge of the servo control track which hasbeen previously recorded on the tape.

Thus as the servo control track deviates from perfect positioningrelative to the read head (servo tracking head), the servo control willactivate and move the servo tracking head to follow the servo track. Themass of the apparatus used for servo tracking should be as small aspossible in order to be responsive and to facilitate very preciseplacement of the servo tracking head.

The head assembly which incorporates the servo tracking head also has atleast one read/write head spaced a precise, predetermined distance fromthe servo tracking head. Thus, whenever the servo tracking head is movedto follow the servo track, the data heads will be moved a like amount.The relative placement of the data tracks with respect to the servotrack is constant, making tracking of the data tracks possible andreliable. Because the tracks, data and servo, are longitudinal to thetape, the tracking motion of the head assembly is perpendicular to themovement of the tape. Movement will be very small in the trackingdirection.

Movement in the coarse mode will be in the same direction, perpendicularto tape movement, but in coarse steps that are defined by a steppermotor and an associated mechanical drive.

Additionally, due to the large amount of data that users may havealready recorded on tapes using tape drives that do not have servotracking capability, it is desirable to accommodate the previouslyrecorded data cartridges. Without backward compatibility, a user will beless motivated to migrate to a servo controlled system.

In order to accommodate the older non-servo tracking data cartridges,the servo tracking cartridges must have an identifier so the tape drivecan recognize the cartridges and their associated formats.

The tape drive also must have the cartridge recognition capabilities,and the capabilities to disable the servo system and permit theoperation of the tape drive in an open-loop mode.

The read/write head of the drive must be accurately and reliablypositioned over the data track of the older non-servo compatiblecartridges. There being no servo track recorded on the earlier leveltapes, the servo mechanism must not function when reading or writing anearlier level data cartridge. The head assembly cannot be allowed tofluctuate, which may be a possibility, whenever not under active servocontrol. If fluctuations occur, the recorded data tracks on the tapewill not be accurately followed by the read/write head; the data may notbe reliably read or may not be recorded in such a manner to be reliablyread at a later time either with the same tape drive or with anothertape drive since the fluctuations of the read/write head cannot bereliably repeated.

The QIC Standard is exemplary of the cartridge and data/servo trackrecording format which has been published. The servo tracks are groupedin two bands that extend over the recording length of the tape. The QICStandard is but one of several possible arrangements and only serves topromote compatibility of data cartridges and the tape drives with whichthey are used.

OBJECTS OF THE INVENTION

It is an object of the invention to lockout the operation of the servotracking assembly to prevent relative movement between the read/writehead and the head positioning carriage of a tape drive.

It is another object of the invention to activate the lockout of theservo actuator by driving both the head carriage and actuator toengagement with the tape drive frame in a first direction and then todeactivate the lockout of the servo actuator by driving the headcarriage and actuator to engagement with the tape drive frame in asecond direction.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and the objects of theinvention are accomplished by the servo tracking carriage and drive ofthis invention.

A carriage is supported for coarse movement in a direction perpendicularto the tape movement path. The carriage is driven by a leadscrew/follower nut arrangement wherein the follower nut is rotated aboutthe screw to provide the necessary drive to cause the nut to movelongitudinally of the screw. The movement of the nut causes the carriageto be driven in a direction parallel to the axis of the lead screw inresponse to a stepper motor rotating the nut. The coarse drive of thestepper motor is used to position the head, and particularly theread/write gap of the head, over the desired data track. The coarsecontrol or open-loop stepper motor control is used exclusively whenreading and writing the uncontrolled data tracks of the early level datacartridges.

Also, in order to accommodate the servo tracking capability control forcartridges with servo tracks, the carriage is provided with aservo-controlled head positioning arrangement. The read/write head issupported on links of a four-bar linkage. The linkage is pivoted on thecarriage and provides a movement of the head in small increments withina shallow arc which substantially parallels the carriage mount pivotpoints. The movement of the head is controlled by a servo controlledactuator, preferably a voice coil motor (VCM), but a piezo-electricdevice or other electrically controllable device could be used. Thefour-bar linkage supports one portion of the VCM with the second portionof the VCM rigidly mounted to the carriage.

Whenever the four-bar mechanism is formed of rigid links, it may be asingle four-bar or a double four-bar mechanism whereby the barssupporting the read/write head extend beyond the carriage pivots to forma second four-bar linkage which reflects the movement of the oppositeend of the linkage assembly. The second four-bar linkage may be used asthe VCM drive portion of the head positioning apparatus. This type ofarrangement has the advantage of removing the VCM from close proximityto the magnetic read/write head and the magnetic tape and therebyreducing strong magnetic flux which could degrade the quality of therecording or reading of the magnetic tape or destroy the recorded dataon the magnetic tape.

The servo control head positioning assembly may be formed of a pair ofbeam springs cantilevered from the carriage with the beam springsattached to the read/write head support or may be joined by anintermediate portion of the material from which the leaf springs arefabricated. The intermediate position serves as a mounting member toattach the beam springs to the carriage. The beam springs may bedeflected to cause the necessary movement of the read/write head tofollow the servo track and thus to follow the data track being read orrecorded.

The deflection of the read/write head and the supporting beam springsmay be accomplished by mounting the coil of a VCM on the read/write headsupport and magnetically displacing the coil relative to the pole piecesdisposed adjacent thereto; or the VCM coil may be attached to a rockerbeam that is pivotally mounted to respond to electrical signals providedto the VCM coil. Movement of the VCM coil translates into movement ofthe rocker beam forcing the head to move, deflecting the ends of thebeam springs.

An alternative approach is to pivot a rigid beam at the midpoint anddispose the read/write head on one end of the beam. The second oropposite end supports the VCM coil. The VCM coil is disposed betweenpole plates of the VCM, and electrical signals provided to the VCM coilwill control the relative position of the coil and the pole plates. Thebar must be long enough to prevent the zenith tilt of the read/writehead from exceeding the maximum allowable during excursions between thelimits of travel necessary to follow the servo track on the tape.

Another approach is to attach a rigid beam member to the back ornon-recording surface of the read/write head. This beam must be of anon-magnetic material and will extend between cantilevered beam springsfrom the read/write head and into proximity of the magnetic pole platesof a VCM. The coil of the VCM is rigidly attached to the beam and may bemoved by the magnetic interaction between the coil and pole plates. Thebeam springs will restrain the tendency to rotate the beam about itsattachment point on the magnetic head and will convert the coildisplacement to a corresponding displacement of the read/write head.This arrangement also could be implemented in a rigid link four-barmechanism in which the mass of the head, beam, coil and four-bar linksis not large enough to restrict the responsiveness required to track theservo tracks.

In order to make the tape drive compatible with older, non-servocartridges, the servo aspect of the carriage must be controllablydisabled. This disabling may be accomplished by blocking movement of themagnetic read/write head, driving the read/write head support to a knownposition, or providing a sufficiently rigid head support that a lock isnot required but the head support may still be deflected in theservo-controlled mode.

A rocker beam which pivots to transfer coil movement to head movementmay be provided with an arm or surface that is engagable by a lock armor locking device which may be pivotally disposed on the cartridge anddetented with respect to the cartridge. The lock/unlock operation may beactuated by driving the carriage to engage the lock arm with a rigidportion of the frame of the tape drive or the bridge supporting thecarriage. Causing the lock arm to pivot into or out of a position wherethe rocker beam is trapped renders the rocker beam immobile and disablesthe servo capability of the tape drive. With the rocker beam immobile,the head is also immobile.

Control of the lockout may be accomplished by reading a controlcharacteristic on the cartridge of a servo tracked cartridge andenabling the tape drive to accommodate the servo track cartridge. Theservo track type cartridge may have an aperture which may be read by anoptical sensor or by a mechanical finger. Alternatively, the surface ofthe magnetic tape cartridge may carry an optically readable codeindicating to the servo control that servo track following is required.For non-servo track tapes, the servo control either may be deactivatedor energized to drive the read/write head against rigid carriagesurfaces.

For servo inhibiting where the VCM is incorporated into the rigid beamdiscussed above, the servo control may drive the VCM to a limit oftravel defined by a stop surface of a portion of the tape drive frameand maintain the VCM coil in that position during open-loop operation.

The use of beam springs, which are sufficiently stiff or rigid to holdthe read/write head against the stiction and dynamic friction forces ofthe tape acting on the read/write head, together with a VCM ofsufficient strength to deflect the stiff beam springs duringservo-controlled operation may eliminate the need for a separate lockoutof the servo mechanism for use with older non-servo cartridges.

A more complete understanding of this invention may be had from theattached drawings and the detailed description of the invention thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a partially disassembled tape drive,having the cover removed for visibility.

FIG. 2 illustrates the carriage assembly exploded to reveal thecharacteristics of the various parts thereof.

FIG. 3 is an exploded view of a second embodiment of the carriage andparticularly the magnetic read/write head positioning control.

FIG. 4 illustrates a four-bar mechanism with a VCM coil for controllingthe location of the read/write head mounted on the back side of theread/write head.

FIG. 5 illustrates a double four-bar linkage with the extended linkscommon to both linkages pivoted on a fixed member, and the read/writehead supported on the ends of the pivoting member on one end and a VCMcoil disposed on the opposite ends of the pivoting members forinteraction with the voice coil magnet plate.

FIG. 6 illustrates the support of a magnetic read/write head oncantilevered beam springs which in turn are supported by a fixed memberof the carriage.

FIG. 7 illustrates an alternative embodiment of a servo mechanismcarriage and servo positioned magnetic read/write head utilizing beamsprings and a VCM.

FIG. 8 illustrates a segment of the carriage of the servo trackfollowing tape drive and a segment of the bridge supporting the carriagetogether with the servo lockout device and its interaction with thebridge.

FIG. 9 illustrates a tape cartridge having a control region indicativeof the servo track recordings on the tape and its capability to be usedwith a servo control read/write head positioning apparatus.

FIG. 10 illustrates a pivot structure which may be advantageouslyincorporated into the rocker beam of the servo control head positioningapparatus.

FIG. 11 illustrates a rigid beam member for translating movement of theVCM coil to the recording head and which may be used as an alternativeto the beam spring support of the magnetic read/write head.

FIG. 12 is an alternative arrangement for the driving of the magnetichead by a VCM in that the magnetic head is suspended on cantileveredbeam springs and the VCM is displaced from the magnetic head to thegreatest extent possible.

FIG. 13 is an embodiment of the actuator where the VCM coil is notrigidly supported but rather is spaced from and stabilized with respectto the VCM magnet by a mass of silicone gel disposed between the coiland the magnet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE BEST

MODE AS CONTEMPLATED BY THE INVENTORS FOR CARRYING OUT THE INVENTION

Referring initially to FIG. 1, there is illustrated a partial tape driveofthe type in which the invention may be used.

FIG. 1 illustrates tape drive 10 with the cover removed for visibilityand with bridge 12 exploded out and removed from the tape drive chassis11. The bridge 12 supports the magnetic read/write head positioningassembly 14. Read/write head positioning assembly 14 is illustrated inFIG. 2 as anexploded view and will be addressed in more detail with thatfigure.

Stepper motors 16 and 18 are supported by chassis 11 of the tape drive10. Read/write head positioning stepper motor 16 through gear 20,preferably aworm gear, provides the positioning drive to position theread/write head positioning assembly 14 relative to bridge 12. Tapecartridge receive/eject stepper motor 18 provides the drive forreceiving and ejecting cartridges (not shown) from the tape drive 10.

Tape drive 10 is further provided with the capstan drive 22 necessary tofeed the tape, not shown. Capstan drive 22 comprises a soft rubber wheelor roller to engage the tape of a cartridge for feeding purposes and isdriven by capstan drive motor 24. The tape drive 10 further includes acartridge sensor 26. Cartridge sensor 26 may be advantageously disposedinan area where no other elements of the tape drive 10 need be presentnor where the cartridge will be resident. Further, cartridge sensor 26is comprised of a pair of electronic elements, typically a lightemitting diode and a photo detector forming a LED photo/receptor pair.The cartridge sensor 26 will be discussed in more detail later.

Referring now to FIG. 2, carriage 30 is illustrated as having a bearingsupport structure 32. Bearing support structure 32 is comprised of apair of arms projecting from carriage 30 and which have grooves formedinto thefacing surfaces thereof to accept bearing 34. Although only onebearing 34 is visible, bearing 34 is duplicated for a substantiallyidentical bearingsupport structure directly below the one illustrated sothat a pair of suchbearings 34 are supported by a pair of such supportstructures 32.

Typically, bearing 34 is molded of a plastic material and is comprisedof acylindrical form 36 having an interior opening 38. The interioropening 38 is characterized by three planar surfaces 40, 42, and 44. Agap 46 in cylindrical form 36 allows the lead screw 48 to be insertedwithin the interior opening 38. In so doing, planar walls 42 and 44 willbe slightly spread apart, widening gap 46. As the cylindrical form 36attempts to close back to its original state, wall 42 will force thelead screw 48 into a positioning engagement with planar surfaces 40 and44, thereby insuring accurate placement of the lead screw 48 relative tobearing 34. Bearing 34 is further provided with a partial flange 50having ribs 52 which will mate with the inner surfaces of bearingsupport structure 32.

Geared nut 54 is threaded onto lead screw 48 and whenever lead screw 48is held stationary by mounting the lead screw 48 into bridge 12, therotationof geared nut 54 by worm gear 20 on the read/write headpositioning steppermotor 16 will cause nut 54 to be progressively raisedor lowered with respect to lead screw 48. The end surfaces 56 of gearednut 54 lie in abutting relationship to the end surface 58 of bearing 34.The force controlling the raising and lowering of the carriage 30 isexerted on the bottom bearing 34 due to the influence of the pre-loadspring 59 which engages carriage 30 and bridge 12 to bias the carriage30 upward. Pre-loadspring 59 maintains contact between geared nut 54 andbottom bearing 34 except when carriage 30 is driven to an end-of-trackposition such as whenthe servo-control latch is activated.

Carriage 30 has a pair of parallel vertical walls 62 and 64. Verticalwalls62 and 64 form a cavity 66 which will be more fully explainedlater. The carriage 30, made of a soft magnetic material, can carrymagnetic flux of a VCM and will aid in controlling stray flux and helpto prevent adverse effects of stray magnetic fields on the magnetictape. If desired, only walls 62,64 need be of a soft magnetic material.Additionally carriage 30 is provided with an anti-rotation boss 31disposed as close to the read/write head 82 as possible to prevent unduerotation of carriage 30 under the influence of spring 59. Anti-rotationboss 31 slideably engages bridge 12 and provides a consistent datumrelative to bridge 12.

To mount the read/write head 82 on carriage 30, leaf spring 68 is formedofthin flat spring stock and is bent to result in a "C" shape or threesides of a rectangle. The middle side 70 of the rectangle 68 is attachedat its ends to cantilevered beam springs 72. Middle section 70 isattachable to vertical wall 62 with epoxy or other suitable adhesives.The free ends 74 of beam springs 72 are attached to attachment bars 76of web 78. Web 78 isformed having a planar section 80 and two attachmentbars 76 and may be integrally molded of plastic or other suitablematerial for ease of fabrication. Attachment bars 76 may be adhesivelybonded or insert molded onto the free ends 74 of cantilever beamsections 72, thereby maintaining a constant spacing between the freeends 74 of springs 72 and adding rigidity to the structure in a twistingmode. The free ends 74 of beam springs 72 may flex up and down even whenattached to the attachment bars 76 of web 78. Planar section 80 servesto space the attachment bars 76 from each other while also providing astructure to route the electrical signal conductors to and from themagnetic head 82. Magnetic head 82 then may be positioned relative toattachment bar 76 and cemented with epoxy orcomparable material to theattachment bars 76. The assembly of leaf spring 68, web 78 and magnetichead 82 provides for limited movement of magnetic head 82 up and down,but it cannot readily be turned about in any other axis or deflected inany other degree of motion.

To effect the movement for magnetic head 82 described above, a VCMcomprising a voice coil 90 and a magnet 86 are provided. A magnet 86 isadhesively attached to the back side 63 of vertical wall 62 withincavity 66. Voice coil 90 is attached using a similar technique to thecoil mounting pad 94 of VCM spring 88.

VCM spring 88 is provided having a mounting pad or attachment pad 92which permits the adhesive attachment of VCM spring 88 to the backsurface 65 ofvertical wall 64 with the voice coil 90 disposed withincavity 66. VCM spring 88 also has an oval span 98 intermediate to theattachment pad 92 and the coil mount pad 94. The oval span 98 providesflexibility and the ability to move the coil mount pad 94 verticallywithin limits with respect to attachment pad 92. By disposing the voicecoil 90 and magnet 86within cavity 66, a closed VCM magnetic circuit isformed and stray or fringing flux is contained close to the VCM and awayfrom the magnetic read/write head 82 and magnetic tape (not shown inFIG. 2).

Extending from the bottom portion of coil mount pad 94 are connectiontabs 96 which serve to accept a connecting material such as an epoxy toconnectthe coil mount pad 94 to the rocker 100 for bi-directionalmovement with the rocker 100.

Rocker 100 is formed as a beam member 102 having a latch arm 104extending from one side thereof. On the opposite end of beam member 102from latch arm 104 is a push bar 106 attached by a flexible support 108.Flexures 110protrude from the sides of beam 102. Flexures 110 made of athin leaf spring material have been formed with tabs 112 to assist inpositioning flexures 110 within slots 114 of carriage 30. Residentwithin slots 114, flexures 110 provide adequate bending capability andcapacity to permit the rocker 100 to oscillate over a limitedoscillation range. Rocker 100 is further provided with recesses 116 intowhich connection tabs 96 are inserted and permanently attached by anepoxy or comparable adhesive material.

Push bar 106 is engagable with and attached to beam spring end 74 ofcantilever beam spring 72 which resides on the bottom of the spring 68.Push bar 106 is cemented with epoxy or comparable material to connectpushbar 106 to the leaf spring 68/web 78/magnetic head 82 assembly. Theflexible web 108 interconnects the end of beam 102 and push bar 106 andprovides mobility to push bar 106 with respect to the end of beam 102,thereby accommodating any slight misalignment which occurs wheneverrocker100 pivots about flexure 110 and does not perfectly follow thetranslation of magnetic head 82. Web 108 further minimizes any forcescaused by the rocker beam 102 which may tend to urge the magnetic head82 away from the magnetic tape surface, thereby preventing degradationof the recording or reading of the data on the tape.

In order to disable the servo control of the read/write head positioningapparatus 14, a lock am 122 is provided. Lock am 122 is mounted oncarriage 30 and rides therewith. Carriage 30 defines a slot 124 whichwillaccept shaft 126 and keeper 128. Keeper 128 and the end of shaft 126are inserted into slot 124 whenever aligned; and then by turning lockarm 122,the keeper 128 will become misaligned with slot 124 and therebyretain lockarm 122 on and movable with respect to carriage 30. Lock arm122 is furtherprovided with a detent arm 130 which carries a detent head132. Detent head132 includes an engaging surface 134 which will matewith and engage detentdepressions 136 on carriage 30. Further providedto lock arm 122 are engagement arm 138 and arm 140.

Referring now to FIGS. 2 and 8, engagement arm 138 may be displaced byengagement with a portion of the bridge 12 of the tape drive 10. Bridge12has stop surfaces 142, 144 onto which engagement arm 138 may be movedto cause pivoting about shaft 126 of the entire lock arm 122. The arm140 when pivoted by engagement arm 138 will engage the undersurface ofrocker latch arm 104. With arm 140 below and in engagement with rockerlatch arm 104, rocker 100 can not freely rotate and is latched.Accordingly the servo tracking movement of magnetic head 82 is disabledand the position of magnetic head 82 and position detent is totallydependent upon the position of the carriage 30. Detent surface 134resides in one or the other of the detent depressions 136. The lower ofthe two detent depressions 136 defines the position of lock arm 122 inwhich the servo mechanism is locked out or disabled. Thus, in order tooperate the lock arm 122 to cause disabling of the servo mechanism, thecarriage 30 must bedriven upward until engagement arm 138 engages thestop surface 144 on the bridge 12. The engagement relationship betweenthe bridge 12 and the carriage 30 with regard to activation anddeactivation of the lock arm 122will become more apparent in FIG. 8 tobe discussed below.

Referring now to FIG. 3, an alternative embodiment of the read/writehead positioning assembly and carriage, the carriage 30 is illustratedwith circular bearing supports 150 instead of the "U" shaped bearingsupports illustrated in FIG. 2. However the bearing support structure ofFIG. 2 could be implemented into this carriage 30, if desired.

Rocker beam 152 is shown with a pivot flexure tab 154. Flexure tab 154and a similar tab on the other side, not visible, may be inserted intoslots 172 of carriage 30 and thereby provide a pivot axis for rockerbeam 152. Rocker beam 152 is further provided with a coil cage 156 whichwill acceptand mount VCM coil 158. Magnetic head support 160 is attachedto the ends of beam springs 162, 164 and further may be used to attach amagnetic head82. The opposite ends of beam springs 162 and 164 areattached to carriage 30, the beam spring 164 attached to a springattachment surface 166 while beam spring 162 is attached to an oppositesurface which is not visible.

With the beam springs, 162, 164 the carriage 30 and the magnetic headsupport 160 all assembled, a mechanism equivalent to a four-bar linkagepermits movement of the magnetic head support 160 and magnetic head 82in one degree of freedom. VCM magnet 168 is shown attached to thecarriage 30in proximity to VCM coil 158, thereby providing thecomponents of a VCM controlling the displacement of magnetic head 82.Rocker beam 152, particularly the outboard end 170 thereof, engagesmagnetic head 82 and with the rocking of rocker beam 152 will cause thedisplacement of magnetic head 82 by a controllable amount.

Referring now to FIG. 4, there is illustrated a simple rigid four-barmechanism which could be used in the carriage 30 of the invention ifdesired. Support 180, a portion of a carriage similar to carriage 30, isprovided with pivot points 182. Pivot points 182 are part of links 184which, in turn, are pivotally attached to magnetic head or head support186. To this point the structure is a classic four-bar linkagemechanism, and movement of the magnetic head/support 186 will result ina movement whereby magnetic head/support 186 remains parallel to theplane defined bythe pivot points 182 as long as links 184 are identicalin length. An extension of support 180, support beam 190, protrudestoward magnetic head/support 186. On the back surface (non-recordingsurface) of magnetic head/support 186 is fixedly attached a pole plate187 and magnet 188 for aVCM. Pole plate 187 and magnet 188 arejuxtaposed with VCM coil 196 mountedon the end of support beam 190 madeof a soft magnetic material. This moving magnet and moving pole designmay be changed to a moving coil design with magnet and pole fixed.Control of the movement of the four-barlinkage including magnetichead/support 186 then may be controlled by an electrical currentprovided to VCM coil 196.

FIG. 5 expands the concept of the four-bar linkage mechanism illustratedinFIG. 4. Support 180 pivotally supports links 192 which, in turn, arepivotally connected to magnetic head/support 186, completing a four-barmechanism. The opposite ends of links 192, which extend beyond support180, are pivotally connected to VCM link 194. Link 194 supports a VCMcoil196. Support 180 has an extension beam 190 protruding outwardlytherefrom and supports on its end face magnet 188 juxtaposed with VCMcoil 196. The advantages of this arrangement, FIG. 5, over thatillustrated in FIG. 4 are in the removal of the voice coil 196 andmagnet 188 from proximity to the magnetic head/support 186 which reducesstray flux near the magnetic head, creates a balanced actuator whichresists shock and vibration, and places fewer design constraints on theelectrically controlled drive.

FIG. 6 is a flexible beam implementation of the servo mechanismillustratedin FIG. 4 with beam springs 198 replacing links 184 in FIG.4. The primary advantage to this arrangement is the elimination of theneed for pivots and rigid links such as illustrated in FIGS. 4 and 5.

Referring to FIG. 7, support 180 either may be separate or may be anintegral part of a carriage such as carriage 30. Support 180 is providedwith anchor points 202 which trap and hold leaf springs 200, 201. Theanchoring of leaf springs 200, 201 at anchor points 202 has the effectof forming two separate leaf springs 200, 201 out of a single piece ofleaf spring material. Each set or branch of the leaf springs 200, 201may be deflected independently of the other. Leaf springs 200 are bondedto and support magnetic head support 160 and in turn magnetic head 82.Leaf springs 201 are attached to and support VCM coil frame 210, whichin turn supports VCM coil 196. Support 180 further supports VCM magnet188 juxtaposed to coil 196. Rocker 204 is a portion of support 180 andis capable of being flexed about flexure point 212. Flexure point 212 isa narrowed section of the material making up a support 180 and rocker204. The ends of rocker 204 are formed into flexures 206 and 208 and maybe attached to the magnetic head support 160 and the VCM coil frame 210,respectively. Attachment of the flexures 206, 208 to members 160, 210 oralternatively integrally forming these members with the rocker 204insuresthat movement of the rocker 204 is translated into positivedisplacement ofthe members to which it is attached or to which it is anintegral part.

Under the influence of a magnetic field created by electric currentpassingthrough VCM coil 196 and interacting with the magnetic field ofVCM magnet 188, one can appreciate that movement of the VCM coil 196will cause a rocking of rocker 204 to displace magnetic head support160.

Reference is now made to FIG. 8. to illustrate a small section of bridge12and a portion of carriage 30. More specifically, the illustration inFIG. 8illustrates the relationship between lock arm 122 and controlsurfaces on bridge 12. Lock arm 122 is totally supported by shaft 126 oncarriage 30. Detent head 132, on detent arm 130 extending along carriage30, engages a detent depression 136. A second detent depression 136 ispositioned closely adjacent and engagable by detent head 132 wheneverlock arm 122 isdisplaced. Engagement arm 138, a part of lock arm 122,extends from shaft 126. As carriage 30 and lock arm 122 are moved upwardand downward as described with reference to FIG. 2, engagement arm 138will engage stop surface 144 and stop surface 142 respectively. As theengagement occurs between engagement arm 138 and stop surface 144 ofbridge 12 and carriage 30 is further driven upward, engagement arm 138will cease to move upward and will cause rotation of lock arm 122 intothe position illustrated in FIG. 8. Conversely, if carriage 30 is drivendownward, engagement arm 138 will engage stop surface 142 and be pivotedin response to continued movement of carriage 30 so that the detent arm130 engages detent surface 136.

Thus by viewing FIG. 8 in conjunction with FIG. 2, it can be seen thatmovement of carriage 30 upward and the engagement of engagement arm 138and stop surface 144 will pivot the lock arm 122 such that the rocker100 will be trapped in a fixed position by arm 140, as is shown,engaging rocker latch arm 104 and holding it against movement. Theunlatching of the rocker 100 is accomplished by driving engagement arm138 into engagement with surface 142 and then driving carriage 30sufficiently pastthat point of engagement to pivot lock arm 122 to thereleased position. The amount of rotation of the lock arm 122 and thespacing of detent depressions 136 need not be large since the amount ofmovement of lock arm122 is small because the amount of movement of therocker 100 is small, encompassing less than one degree of rotation.

Referring now to FIG. 9, which illustrates and outlines a magnetic taperecording cartridge 220 and which exposes a span of magnetic tape 222,there is found in the lower right hand corner an indicia region 224. Anindicia region 224 which may take several forms. The indicia region 224may be an opening extending all the way through the cartridge in thisregion; and whenever positioned in the tape drive 10, the indicia region224 will be disposed between the parts of a cartridge sensor 26illustrated in FIG. 1.

Alternatively, region 224 could be an aperture in either the top surfaceorthe bottom surface of the cartridge 220 which would accept amechanical sensing finger which could be moved into engagement with thecartridge. The opening would allow the sensor finger to protrude intothe volume of the cartridge to indicate that the cartridge is a servocartridge and the cartridge and the servo mechanism of the tape drive 10would need to be enabled.

In older level cartridges this region 224 would not exist and,accordingly,any attempt to sense it would result in a conclusion thatthe cartridge wasan older, down-level open-loop stepper motor controlcompatible cartridge. Thus the servo mechanism of the present inventionwould need to be disabled, overridden, or locked out prior to theattempt to read or write the data from or to the magnetic tape 222.

Referring now to FIG. 10, a pivot leaf spring 226 is illustrated. Pivotleaf spring 226 is comprised of a plurality of segments, particularlyflexures 110 and flexure tabs 112. Extending from beam 228interconnectingflexures 110 are beams 230 and 232. Beam 230 providessignificant area in which plastic of the rocker 100 as shown in FIG. 2may be incorporated. This flexure spring 226 and particularly beams 230,232 and the portion ofbeam 228 between flexures 110may be insert moldedinto plastic. The push bar 106 of rocker 100 then may be insert moldedaround the end of tab 234 with tab 234 providing the web 108 describedearlier with respect to FIG. 2.

The formation of the flexure leaf spring 226 and its incorporation intorocker 100 by insert molding enhances the precise control and theresilient return movement of rocker 100 and the movement of VCM coil 90and magnetic head 82 in FIG. 2.

Further alternatives in the design of the magnetic head positioningapparatus incorporating a servo mechanism are illustrated in FIGS. 11and 12. Referring now to FIG. 11, there is illustrated an alternative tothe carriage 30 and the head positioning assembly 14 carried by carriage30 illustrated in FIG. 2. Carriage 240 is provided with bushings 242through which a lead screw essentially the same as lead screw 48 of FIG.2 can be extended. Bushings 242 will trap a geared nut identical to oranalogous togeared nut 54 of FIG. 2 to cause the carriage 240 to beelevated and depressed to select the general region positioning of themagnetic head 244. Beam 246 is provided with a VCM coil 248 fixed anddisposed on beam 246. VCM coil 248 is disposed intermediate VCM poleplate/magnet assembly 250 to complete magnetic circuit of the VCM. Beam246 is formed with an aperture 252 which accommodates a living hinge256. Living hinge 256 interconnects a mounting member 258 and carriagetabs 260. Carriage tabs 260 are inserted into notches 262 on carriage240 and act to precisely position the living hinge pivot member 254relative to the carriage 240.

The apparatus shown in FIG. 11 has the advantages of simplicity, ease inmanufacturing and may be disabled from a servoing operation with theprovision of a constant electrical voltage to the coil 248 effectivelypositioning the head 244 in a single position relative to carriage 240.Pole plates/magnet assemblies 250may be fixed to and carried by anextension of carriage 240 or fixed to a portion of the tape drive frame.The position of the coil 248 and head 244 may be defined by theelectricalvoltage to the coil 248 or by driving the beam 246 and head244 to a hard stop in the open-loop mode (not shown).

The desirable aspect of displacing the VCM as far away as possible fromthemagnetic head 244 is accomplished by the mechanism of FIG. 11. Solong as beam 246 is of sufficient length to limit the amount of zenithtilt to less than 1/4 degree maximum throughout the excursion of themagnetic head244 between its limits of travel, this oscillating orpivoted beam arrangement is acceptable.

FIG. 12 is an illustration of a further alternative embodiment where thesupport 180 provides the support or base for cantilevered beam springs198. Cantilevered beam springs 198 are attached at their free ends tomagnetic head/support 186. Beam 270 is cantilevered from thenon-recordingsurface of magnetic head/support 186 and extends towardsupport 180 and supports VCM coil 196 juxtaposed to VCM magnet 188attached to support 180of a soft magnetic material. Cantilevered beamsprings 198 will resist any effort by the VCM components 196, 188 totwist cantilevered beam 270 and thus will cause the upward and downwardmovement of cantilevered beam 270 along with magnetic head 186. Further,the cantilevered beam springs 198 will act as links of a four-barlinkage thereby insuring that the magnetichead/support 186 will remainsubstantially parallel to the support 180 during its movements.

The advantage of this arrangement is the displacement of the VCM awayfrom the magnetic head/support 186.

Referring to FIG. 13, the actuator assembly of FIG. 7 is illustrated inmodified form. The VCM coil 196 and VCM coil frame 210 are not supportedby leaf springs or other structure as found in FIG. 7 The VCM coil 196andVCM coil frame 210 are connected to rocker 204 at flexure 208, butare not stable. In order to stabilize VCM coil 196 and VCM coil frame210 relativeto the actuator support 180 and VCM magnets 188, a smallquantity of visco-elastic material such as a silicone gel 214 isdeposited between andin contact with VCM coil 196/VCM coil frame 210 andVCM magnets 188. The silicone gel 214 when cured will adhere to the VCMcoil 196/VCM coil frame210 and VCM magnets 188 stabilizing the coil196/frame 210. The resilient characteristics of the silicone gel 214permits the displacement of the coil 196/frame 210 relative to actuatorsupport 180 and magnets 188.

A similar result may be had by removing attachment pad 92 and oval span98 of VCM spring 88 in FIG. 2 and inserting silicone gel 214 betweencoil mount pad 94 and magnet 86 and curing the silicone gel.

The operation of the read/write head positioning assembly of FIG. 2 hastwopossible modes of operation: one being in the servo control mode, andthe other being in the open-loop stepper motor mode.

For the open-loop stepper motor mode, upon detection of cartridge of acartridge 220 without an indicia region 224 or equivalent activatingcharacteristics, the carriage in FIG. 2 and FIG. 8 is driven by thestepper motor 16 in an upward direction until lock arm 122 is shifted toaposition whereby the arm 140 of lock arm 122 engages and traps therocker latch arm 104, thus stabilizing the magnetic head 82 with respectto carriage 30. Thereafter, stepper motor 16 drives the geared nut 54 toraise and lower carriage 30 to position the read/write head 82 over adatatrack. The carriage 30 remains in that position so long as the samedata track is being accessed by the read/write head 82, thereafter theaccessing of various tracks on the magnetic tape is accomplished bydriving stepper motor 16 a predetermined number of steps to incrementthe magnetic read/write head 82 to a position where it will correspondwith the predetermined position of a selected magnetic track on themagnetic tape in a cartridge.

Assuming that the tape drive 10 has most recently operated in anopen-loop stepper motor accessing of tape tracks and the servocompatible cartridge 220 is inserted into tape drive 10, the cartridgesensor 26 will detect the characteristic of indicia region 224 of thecartridge 220 and will signal the electronic controls of the tape drive10 to drive the carriage 30 downward until the lock arm 122 engages stopsurface 142 rotating lock arm 122 to disengage from the rocker latch arm104. Once the rocker latch arm 104 has been freed, rocker latch arm 104and rocker 100 are free to bemoved and influenced by the movement of VCMcoil 90. Thereafter carriage 30either is incremented to its firstposition for accessing a desired data track or the read/write gap of themagnetic head 82 is placed in proximityto the desired data track and aread only gap on the magnetic head 82 is placed in proximity of a servotrack recorded on tape 222 of cartridge 220. The read only gap of themagnetic head 82 will sense the servo track and provide an electricalsignal to the servo control circuitry of the tape drive 10. The servocontrol circuitry in turn will provide a drive signal of controlled butvariable voltage to the VCM coil 90 creating a magnetic field which willinteract with the magnetic field generated by the VCM magnets 88. Themagnetic fields interacting will move the coil 90 a small amount thuspositioning the magnetic head 82 with its read gap tracking the servotrack of the tape 222 and read/write gaps following thedata tracks ontape 222. As the read only gap is moved, the electrical signal generatedby it indicating its position relative to the servo trackon the magnetictape 222 will vary causing a variance of the signal provided to the coil90 of the VCM.

Due to the control over the position of the magnetic head 82 relative tothe magnetic tape 222, and relative to the servo tracks and data tracksrecorded thereon, a magnetic tape with a much higher density recordingpattern may be utilized whenever in the servo control mode. The signalsderived by the servo electronics from the magnetic read head gapprovided to the VCM coil may be provided by a conventional electronicservo circuitry and therefore need not be described in detail.

Alternative approaches to the physical latching or disabling of rocker100 include the electrical energization of the VCM at a constant voltageto hold the voice coil in a fixed position relative to the carriage, ineffect creating a fixed position for the read/write head relative to thecarriage.

While various embodiments of various portions of this tape drive havebeen disclosed, it will be recognized that one of skill in the art maymake minor variations and modifications to any or all of the variousembodiments without removing the apparatus from the scope of theappended claims which define the invention.

We claim:
 1. A tape drive system for recording and reading data storedon a storage tape in a tape cartridge, said cartridge being either oneof a first cartridge type having no servo control tracks on the tapetherein, or a second cartridge type having a tape therein with servocontrol tracks recorded thereon, said second cartridge having servocontrol indicia comprising a control region indicating a presence ofsaid servo control tracks;said tape drive system comprising; a frame,said frame supporting a sensor for detecting said control region; adrive motor and a capstan; a magnetic head; and a head positioningactuator for moving said magnetic head parallel to said tape andperpendicular to a direction of movement of said tape when driven bysaid capstan; said head positioning actuator comprising:a carriage and amotor for positioning said carriage for coarse positioning of saidmagnetic head; a servo drive for fine positioning of said magnetic headusing servo signals, said servo drive comprising a voice coil motor; arigid member engaged with said carriage, said magnetic head, and saidservo drive, and is displaceable by a component of said voice coil motorrelative to said carriage, whereby displacement of said head is effectedby said displacement of said rigid member;a displaceable latch connectedto said carriage and engageable with said rigid member for immobilizingsaid rigid member against movement relative to said carriage, saiddisplaceable latch is responsive to a condition indicating the absenceof said servo tracks on said tape, detected by said sensor; wherebydisplacement of said magnetic head relative to said carriage isprevented when said displaceable latch is engaged with said rigidmember, thereby rendering said actuator and said tape drive systemcompatible with cartridges not having servo tracks recorded on the tapewithin the cartridge.
 2. A tape drive system for recording and readingdata stored on a storage tape in a tape cartridge, said cartridge beingeither one of a first cartridge type having no control indiciaidentifying servo tracks on the tape therein and a second cartridge typehaving a tape therein with servo control tracks recorded thereon, saidsecond cartridge type having servo indicia comprising a control regionindicating presence of said servo control tracks;said tape drive systemcomprising:a frame, said frame supporting a sensor for detecting saidcontrol region; a drive motor and a capstan; a magnetic head; end a headpositioning actuator for moving said magnetic head parallel to said tapeand perpendicular to a direction of movement of said tape when driven bysaid capstan; said head positioning actuator comprising:a carriage and amotor for positioning said carriage for coarse positioning of saidmagnetic head; a servo drive for fine positioning of said magnetic headusing servo signals, said servo drive comprising a voice coil motor; arigid member engaged with said carriage, said magnetic head, and saidservo drive, and displaceable relative to said carriage by a componentof said voice coil motor, whereby displacement of said head is effectedby said displacement of said rigid member; wherein said means forholding comprises a displaceable latch engageable with said rigidmember, thereby immobilizing said magnetic head; whereby displacement ofsaid magnetic head relative to said carriage is prevented when saiddisplaceable latch is engaged with said rigid member, thereby renderingsaid actuator and said tape drive system compatible with cartridges nothaving servo tracks recorded on the tape within the cartridge.
 3. Thetape drive system of claim 2 further comprising a drive for displacingsaid actuator relative to said storage tape to and from fixed positionscorresponding to data tracks on said storage tape of said cartridge. 4.The tape drive system of claim 2 further comprising a stepper motor; agear driven by said stepper motor; a lead screw and mating nut, saidmating nut drivingly engaged with said carriage to displace saidcarriage relative to said lead screw, said lead screw supported by saidframe.
 5. The tape drive system of claim 4 wherein said latch isdisplaceable from a first engaged position to a second disengagedposition by movement of said carriage being driven to a firstend-of-travel position by said stepper motor, said latch engaging afirst surface on said frame prior to said carriage arriving at saidend-of-travel position, thereby shifting said latch from said firstposition to said second position during a final portion of saidmovement.
 6. The tape drive system of claim 5 wherein said latch isdisplaceable from said second disengaged position to said first engagedposition by movement of said carriage being driven to a secondend-of-travel position by said stepper motor, said latch engaging asecond surface on said frame prior to said carriage arriving at saidsecond end-of-travel position, thereby shifting said latch from saidsecond position to said first position during a final portion of saidmovement.